1. Field
The present disclosure relates generally to power converters and, more specifically, to power converters utilized with dimmer circuits.
2. Related Art
Residential and commercial lighting applications often include dimmers to vary the brightness of the outputted light. A dimmer circuit typically disconnects a portion of an alternating current (ac) input voltage to limit the amount of voltage and current supplied to an incandescent lamp. This is known as phase dimming because it is often convenient to designate the position of the dimmer circuit and the resultant amount of missing voltage in terms of a fraction of the period of the ac input voltage measured in degrees. In general, the ac input voltage is a sinusoidal waveform and the period of the ac input voltage is referred to as a full line cycle. As such, half the period of the ac input voltage is referred to as a half line cycle. An entire period has 360 degrees, and a half line cycle has 180 degrees. Typically, the phase angle is a measure of how many degrees (from a reference of zero degrees) of each half line cycle the dimmer circuit disconnects. On the other hand, the conduction angle is a measure of how many degrees (from a reference of zero degrees) of each half line cycle the dimmer circuit does not disconnect a portion the ac input voltage. In other words, the conduction angle is a measure of how many degrees of each half line cycle in which the dimmer circuit is conducting. In one example, the removal of a quarter of the ac input voltage in a half line cycle may correspond to a phase angle of 45 degrees but a conduction angle of 135 degrees.
Although phase angle dimming works well with incandescent lamps that receive the altered ac input voltage directly, it typically creates problems for light emitting diode (LED) lamps. LED lamps often require a regulated power converter to provide regulated current and voltage from the ac power line. Most LEDs and LED modules are best driven by a regulated current, which may be provided by a regulated power converter from an ac power line. Dimmer circuits typically don't work well with conventional regulated power converters and their respective controllers. Regulated power converters are typically designed to ignore distortions of the ac input voltage and to deliver a constant regulated output. As such, conventional regulated power supplies would not satisfactorily dim the LED lamp. Unless a power converter for an LED lamp is specially designed to recognize and respond to the voltage from a dimmer circuit in a desirable way, a dimmer is likely to produce unacceptable results, such as flickering or shimmering of the LED lamp with large conduction angles and flashing of the LED lamp at low conduction angles.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.